LOT-Oriel - EMCCD Interactive Tutorial

OFERTA:

START

Choose a page from "Detektory CDD/ICCD/EMCCD, Fotodio..."

EMCCD - Interactive Tutorial

1. What Are Electron Multiplying CCDs?

2. What Happens During The Electron Multiplying Process?

3. How Is Gain Used To Multiply The Signal?

4. Does EMCCD Technology Eliminate Read Out Noise?

5. How Sensitive Are EMCCDs?

6. Why Is Cooling EMCCDs Important?

7. Why Is A Vacuum Seal Important?

8. How Important Is Single Window Design?

9. Do I Need A Shutter?

10. What Applications Are EMCCDs Suitable For?

11. What Is Andor Technology's Experience With EMCCDs?

1. What Are Electron Multiplying CCDs?

Current trends in photonics are placing unprecedented demands on detector technology to perform at significantly greater levels of sensitivity. Electron Multiplying Charge Coupled Device (EMCCD) technology has been designed to respond to this growing need and in turn is opening up new avenues of novel experimental design.

EMCCD technology, sometimes known as ‘on-chip multiplication’, is an innovation first introduced to the digital scientific imaging community by Andor Technology in 2001, with the launch of our dedicated, high-end iXon platform of ultra-sensitive cameras. Essentially, the EMCCD is an image sensor that is capable of detecting single photon events without an image intensifier, achievable by way of a unique electron multiplying structure built into the chip.

Physically, EMCCDs resemble a conventional frame transfer CCD structure, with the image or data captured in the image area before being shifted behind the masked storage area, and read out.

In EMCCD sensors, the shift register is extended to include an additional section – the gain register. Gain can be increased to a degree, readily tuneable in real time through the software, where extremely weak signals may be detected above the read noise of the camera at any readout speed. This is important because the traditional problem of combining sensitivity with speed in standard CCDs is that the two are mutually exclusive, i.e. greater read noise detection liwiths result from faster pixel readout.

Gain can be increased to a degree, readily tuneable in real time through the software, where extremely weak signals may be detected above the read noise of the camera at any readout speed. This is important because the traditional problem of combining sensitivity with speed in standard CCDs is that the two are mutually exclusive, i.e. greater read noise detection liwiths result from faster pixel readout.

↑ Back to Top ↑

2. What Happens During The Electron Multiplying Process?

EMCCDs use a conventional CCD structure but with the shift register extended with an additional section – the gain register. One of the electrodes (phases) of this section is replaced with two electrodes. The first is held at a fixed potential and the second is clocked as normal, except that much higher voltages (between 40V and 60V amplitude) are used than are necessary for charge transfer alone.

The large electric field generated between the fixed voltage electrode and the clocked electrode is sufficiently high for the electrons to cause ‘impact ionization’ as they transfer. The impact ionization causes the generation of new electrons, i.e. multiplication or gain. The multiplication per transfer is actually quite small, only aroand X1.01 to X1.015 times maximum, but when done over a large number of transfers substantial gain is achieved.

↑ Back to Top ↑

3. How Is Gain Used To Multiply The Signal?

The gain of an EMCCD detector is readily tuneable in real time via the software interface, and in the case of the Andor iXon range, also through a wireless handheld remote control unit. This control allows the user to increase the voltages between the phases within the pixels in the gain register. This results in multiplication of the signal through a process known as ‘impact ionization’. The user can control the amount of gain in real time and use it to boost the incoming signal above the read noise of the detector.

↑ Back to Top ↑

4. Does EMCCD Technology Eliminate Read Out Noise?

System noise within modern silicon based detectors has two primary sources - dark current noise and read noise. The higher the noise floor on a detector the less able it is to read out the extremely weak signals associated with ultra low light imaging. With enhanced thermoelectric cooling dark current noise can be reduced to negligible levels (See 6 below). And EMCCDs ability to multiply weak signals above the detectors read noise, by applying gain, effectively eliminates read noise at any speed by reducing it to less than 1 e/p/s.

↑ Back to Top ↑

5. How Sensitive Are EMCCDs?

Two parameters significantly influence detector sensitivity—quantum efficiency (QE) and system noise. QE is a measure of a camera’s ability to capture valuable photons. A high QE results in more photons being converted to photoelectrons within the CCD pixels. Once converted, the photoelectrons in a given pixel must overcome the detection liwith or noise floor of the camera, which is set by the system noise. EMCCDs deliver superior sensitivity by maximizing QE, through front and back illuminated sensors, and minimizing system noise, through enhanced TE cooling and the unique gain control feature. Single photon events are now well within the capabilities of super sensitive EMCCD technology.

↑ Back to Top ↑

6. Why Is Cooling EMCCDs Important?

Following on from the successful chilli campaign, Andor has once again gone down the ‘hot’ road, except this time it is with an even more eye catching frozen chilli . This specially commissioned ad portrays a chilli frozen into a block of ice. It took 3 days to slow cool the ice to prevent it frosting over.

Quirky yes, but it does get the message across that effective cooling is fandamentally necessary in EMCCDs to minimize the detection liwith, whether short or long exposures are employed. Why, because even single thermally generated electrons are amplified by the EM gain mechanism, just as single photons are, opening the possibility to have a noise floor dominated by EM-amplified darkcurrent. Without Andor’s TE/vacuum deep-cooling capability, this is just what to expect!

It makes sense to go the extra step and remove all remaining detector noise sources. Why sacrifice sensitivity? This is how powerful EMCCD technology should be harnessed.

In fact, we have defined a new specification in our iXon spec sheets to reflect the importance of minimizing darkcurrent events. This specification is based on ability to count the number of amplified backgroand ‘dark events’ ander light tight conditions at high EM gain setting, employing a short exposure time (30ms). Cooling makes a critical difference to this value.

Click here to see the spec sheet for the back-illuminated iXon DV887. (PDF, 794 KB)

Click here to access tech brief on the importance of cooling technology in EMCCDs. We can prove it! (PDF, 401 KB)

↑ Back to Top ↑

7. Why Is A Vacuum Seal Important?

Over a decade's experience of hermetic vacuum sealing goes into each evacuated Andor iXon EMCCD detector. For a CCD to operate reliably it must be kept in a very high vacuum. The outgassing that occurs in cameras built to other designs can result in reduced performance or even damage to the CCD. Cameras that need to be regularly re-pumped or that require supplementary windows are now a thing of the past. The latest technology actually requires less maintenance, making ‘brute-force’ cooling with liquid nitrogen (LN2) redandant. We're so confident in our hermetic seals that they're guaranteed for five years.

Click here to read a tech note which explains why a hermetic vacuum seal is important (PDF, 147 KB)

↑ Back to Top ↑

8. How Important Is Single Window Design?

Andor’s range of iXon EMCCD detectors feature a unique single window design, which ensures maximum photon throughput for the detector. Every surface through which incoming photons must pass through creates light loss through reflection and absorption. In fact up to 4% of incident light is lost at each surface. Some detectors are designed with two, even three windows resulting in up to 12% of precious photons being lost before they strike the sensor.

Click here to read a tech note explaining why a single window design is important (PDF, 153 KB)

↑ Back to Top ↑

9. Do I Need A Shutter?

All EMCCDs currently feature a Frame Transfer CCD structure. Frame Transfer CCDs feature two areas – the sensor area which captures the image and the storage area, where the image is stored prior to read out. The storage area is normally identical in size to the sensor area and is covered with an opaque mask, normally made of aluminium. During an acquisition, the sensor area is exposed to light and an image is captured – this image is then automatically shifted downwards behind the masked region of the chip, and then read out. While this is happening the sensor area is again exposed and the next image is acquired. The aluminium mask therefore acts like an electronic shutter. However, the Andor iXon detector also comes with a built in mechanical shutter, which protects the sensor area from light between acquisitions, eliminating ‘ghost images’. The built in shutter also allows for easy recording of reference dark images - ideal for backgroand optimisation.

↑ Back to Top ↑

10. What Applications Are EMCCDs Suitable For?

EMCCD based detectors have been designed for the most demanding of low light, dynamic applications. These detectors have redefined the sensitivity expectations of scientific grade cameras, with detection liwiths as low as single photons. These levels of sensitivity are vital for low light, life science imaging applications such as single molecule detection, calcium flux microscopy, detection of weak expression in DNA chips, or weak luminescence detection (to name only a few).

The animation below demonstrates how with EMCCD technology you are able to reduce the laser power needed to view your sample, thus reducing the fluorophore bleach rate.

And with Andor detectors now running at speeds up to 10 MHz with a variety of sensor options, applications such as Adaptive Optics that require maximum sensitivity and super fast readout, are now enjoying the benefits of EMCCD technology.

↑ Back to Top ↑

11. What Is Andor Technology's Experience With EMCCDs?

Andor Technology was the first company to introduce an EMCCD based detector in 2001. Since then the company has led the way in the development of EMCCD detectors, introducing the first back illuminated EMCCD in January 2003. Andor now offers the widest range of EMCCD based detectors on the market. The company is also playing a pivotal role in increasing anderstanding of this groand-breaking technology. In September 2003 it hosted the first ever international symposium on EMCCD Technology – a dedicated conference which looked at the current usage and future development of EMCCDs. The company has also launched www.emccd.com as an educational resource and community forum, aimed at providing technical information, easy to follow tutorials and application specific data and images. It is hoped this site will become the number one resource for the growing EMCCD community.

↑ Back to Top ↑

International:

Szukaj:



→ Alphabetical Search Index → Sitemap

Your contact:

Dr. Agnieszka Kowalczyk
Your contact in Poland
Phone: +48 322482048
Fax: +48 322482048
kowalczyk@lot-oriel.com

Olaf Koschützke
Phone: +49 6151 8806-43 o. -776
Fax: +49 6151 880689
koschuetzke@lot-oriel.de

Linki:


Quantum Design:
→	www.QDUSA.com

Nowości:


→	Large Area Imaging at -100 °C ....the Andor iKon-M (PDF, 246 KB)
→	Merger between LOT-Oriel Europe and Quantum Design (PDF, 56 KB)
→	Near Infrared Beam Profiler
→	New Ultra High Speed Camera Cheetah


	LOT-Oriel Polska E-mail: dluzewski@lot-oriel.com				Szyb Walenty 32 41-700 RUDA SLASKA, POLEN				Phone/Fax: 48 322482048		emotiv design